I'm re-reading Lord of Chaos at the moment and in that, there's much talk in Salidar about the "new weaves" Nynaeve and Elayne have come up with (mainly from Moghedien). It's mentioned that one sister believes the weave for eavesdropping could be tweaked to allow communication over long distances. It seems unlikely that this would be casually dropped in and then never mentioned again - but then there's been plenty of time for it to be developed by now. I assume, once miscommunication stops serving the story (which it should by aMoL), we'll see some of these options put into practice.